Operating systems

manages peripherals provides security controls access provides a platfrom to run software utilities for system management allows multi-tasking

CLI GUI

windows icons/images menus pointers

command lines in termals and etc

usernames and passwords priviledge policys i.e student can only view their files but teacher can view their students files.

the centre of the operating system directly interacts with the hardware

distributed multi-user multi-tasking embedded real time

a distributed system uses multiple processors physicallly seperated to split tasks among them more powerful tasks completed quicker

allows multiple users to be on he server at once without security issues used when resources need to be accessed simulatneously

allows multiple programs to run at once never actually at once but appears like it

pages are all fixed sizes physical divisions i.e splits memory into 4Kbs and splits the program in the same intervals

segments are sections of the program logical divisions in order to fit free spaces

scheduling controls how the processor time is allocated which allows for multi-tasking

round robin first come first server shortest job first shortest time remaining job shortest time remaining multi-level feeback queue

processor time divided equally among jobs given time slices

low wait time doesnt scale well more taskes smaller time slices less efficient

first job in is processed then move ot the next

processes may have to wait a long time

the job that requires the shortest processor time is completed first

the job which requires the shortest processor time left is completed first

reduces wait time (the long jobs are done last) can cause starvation

more efficient than shortest job first can still lead to starvation

uses queues where each task has a priority if a process uses to much processor time given low priority if sat idel for too long priority is moved up

an interrupt is a way to signal to the CPU that a task needs the CPUs processor time